Frameless spectacles have been in the market for some years. This type of spectacles boasts the desired characteristics of lightweight due to the fact that there is no encircling material around the lenses. Lenses, therefore, are bolted to the spectacles frame by screws through the pre-drilled holes on the lenses. Present invention will refer to such frameless spectacles as “direct bolting” spectacles, to avoid the confusion caused by the term frame, which is used pervasively in this application.
The typical embodiment of such lightweight spectacles consists of bolting the two lenses to the central bridge, which has a pair of nosepad arms welded to the central bridge. On the outer side of the lenses, side arms (going through temple area and resting on top of human ears) are bolted to the lenses, also using screws.
To ensure and enhance the desired attribute of lightweightness, latest generations of direct bolting spectacles use lightweight alloys containing, for example, titanium and other metals for the frame material. To add the nosepad support arms to the central bridge, however, welding is needed to join the nosepad support arms to the central bridge.
Distance between welding points on the direct bolting spectacles, for welding the nospad arms to the central bridge of spectacles frame and for welding other components such as screw, described later, is often times as small as 2 to 3 mm (millimeters). Such limited room for welding caused a higher rejection rate off the production line by QC (Quality Control), and therefore increased costs of production, due to failure to meet the precision requirement in welding. The increase costs of production in the industry no doubt will be reflected in the products sold into the stream of commerce.
Due to the resulting high temperature needed for achieving effective welding, some variation of the elasticity of the alloy material consisting the frame will occur and adversely affect the durability of the frame.
The use of titanium alloy further exacerbates the welding defects because titanium is inherently harder to weld than traditional carbon-steel alloy, or copper-zinc alloy, or the mixture thereto.
Another problem the direct bolting spectacles has is the use of screws to fit lenses to the frame. Proper amount of torque must be applied to the screws when fitting the lenses to the frame. Too tight, the lenses will be under constant stress and have higher tendency to break. Too lose, the lenses are not properly secured to the frame and the spectacles might fall apart unexpectedly; and further that the focus of the lenses might be different from the predetermined positions by optometrist or ophthalmologist, causing straining injury to the eyes.
Besides the issue of imprecision torque to the screws when fitting lenses to the frame, the welding of the tiny screws onto frame is itself another industry problem. These tiny screws present the same type of precision welding challenges to the production facility.
In addition to welding defects that are found at the production line, latent welding defects (both on the nosepad arms and on the welded screws) do not manifest themselves until the spectacle frames, already passed QC, get used for some time and then consumers start to feel something wrong with the frame. This type of latent defects further result in increase costs of consumer service, product return and even product reliability on the market.